1. Field of the Invention
The invention relates to an optical device, and more particularly to an optical device having lens frames positioned by springs.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional optical lens 100 includes a base 10, a first lens frame 20, a second lens frame 30 and a third lens frame 40. An image sensing element (not shown) is disposed on the base 10. The first lens frame 20 bears a first lens group (not shown). The second lens frame 30 bears a second lens group (not shown). The third lens frame 40 bears a third lens group (not shown). The first lens frame 20 has two first pins 22 on an outer periphery thereof. The second lens frame 30 has two second pins 32 on an outer periphery thereof. The third lens frame 40 has two third pins 42. In zoom operation, the first pins 22, the second pins 32 and the third pins 42 are driven by cam grooves on a cam barrel and guided by the guiding grooves on a straight advance barrel to move toward or apart from the image sensing element on the base 10 along an optical axis.
There are gaps existing between the first pins 22, the second pins 32, the third pins 42 and the cam grooves. The gaps may cause inaccurate positioning of the lens frames so as to cause imprecise zooming. To fix the problem, the optical lens 100 further includes a first spring 50, a second spring 60 and a third spring 70. The first spring 50 connects the first lens frame 20 and the base 10 and exerts a spring force on the first lens frame 20. The second spring 60 connects the second lens frame 30 and the base 10 and exerts a spring force on the second lens frame 30. As a result, the first pins 22, the second pins 32 and the third pins 42 are pulled by the first spring 50, the second spring 60 and the third spring 70 that are extension springs to abut the cam grooves 112, 114 and 116 as shown in FIG. 3.
In the described structure, each lens frame is connected to the base by an extension spring. Therefore, three extension springs are included in the optical lens 100, the assembly of which requires much time and labor.